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Old Dec 11, 2006, 07:56 PM
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Troutdale, Oregon, United States
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6 bladed prop

Well, here I go again, looking for the impossible. Has anyone ever made their own? Could 2 -3 blades props be combined? I am open to any and all ideas but am deadly serious on finding a solution.
peter
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Old Dec 11, 2006, 08:17 PM
Good Better Best quest.
olmod's Avatar
Australia, VIC, Cranbourne East
Joined Apr 2004
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Its deffinately possible, one recently in groups posted but i cant remember who
but it does require building a accurate jig to mill saw the correct angles when cutting up the hubs of the props then they were clamped together using 2 turned lipped washers that were notched around the circumference for the blades to poke through so the prop hub was completly encapsulated.
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Old Dec 11, 2006, 08:28 PM
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United States, NJ, Frenchtown
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You are modifing the crap out of a safe 2 props by leaving sharp edges that can shatter without any warning at any rpm.

Non running, fine.

Flying, your lawsuit at a flying field.

Can you balance it for running balance ?

EDIT.

What plane used 6 bladed props ?
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Old Dec 11, 2006, 09:35 PM
Good Better Best quest.
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OK so your a nay sayer that still does not say it cant be done safely,no rpm figure has been discussed,vario prop seem to do it ok with 4 blades.
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Old Dec 12, 2006, 02:08 AM
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East Anglia, UK
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Quote:
Originally Posted by peterpont
Well, here I go again, looking for the impossible. Has anyone ever made their own? Could 2 -3 blades props be combined? I am open to any and all ideas but am deadly serious on finding a solution.
peter
Sure. I've designed lots pf props to make yourself..

http://www.rcgroups.com/forums/showthread.php?t=585380

I guess I could do a 6 blader if you asked me nicely..

Hub area would be the tricky bit..Also RPm would be a tricky thing..if you go low enough its safe.
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Old Dec 12, 2006, 03:12 AM
hul
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Quote:
Originally Posted by olmod
Its definitely possible, one recently in groups posted but i cant remember who
Lynxman? Starting at post #312 http://www.rcgroups.com/forums/showt...ight=propeller

Hans
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Old Dec 12, 2006, 03:22 AM
Light and floaty does it
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Cambridge, Great Britain (UK)
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Quote:
Originally Posted by cyclops2
What plane used 6 bladed props ?
Some big turboprops. The newer Hercules variants certainly have them.
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Old Dec 12, 2006, 03:40 AM
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Christchurch, New Zealand
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The hub is the problem... you could use varioprop blades, or perhaps heli tail blades.

ATR airliners have 6-bladers, as well as the hercs.
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Old Dec 12, 2006, 03:46 AM
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An all wood solution is possible..if the power levels are not too high...which they will not be if its a true scale prop. Generally you end up with pretty low RPM and pretty coarse pitch.

Milling up a varioprop type hub in metal is quite an undertaking..
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Old Dec 12, 2006, 03:58 AM
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True... however, a hexagonal core block to which you could screw six T-Rex tail blade grips wouldn't be too bad, nor would the fitting to do the job of the 'rex's pitch slider.

And since a T-Rex tail does 19000 RPM stock, it's going to be pretty strong even if you use the plastic grips. I think it's a runner, but you'd only get something like a 6" diameter. Motocalc tells me a 6 blade 6x4 takes around 400W at 15000 RPM and creates a kilogramme of thrust; not shabby performance.
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Old Dec 12, 2006, 04:26 AM
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Oh..6" is not an issue..I was assuming it as 10-12" diameter..I wouldn't want to run that much over 5000..
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Old Dec 12, 2006, 04:31 AM
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Christchurch, New Zealand
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Well, for bigger you'd want to do the same thing, but with T-Rex 600 or Raptor blade grips. Really big, I guess you could use main blade grips... but that's getting silly, you'd need 2500W to turn a 6-blade heli head using 325mm blades...
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Old Dec 12, 2006, 10:38 PM
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Troutdale, Oregon, United States
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6 blade prop

WoW! Great response from knowledgable people. I am in the process of building a 5% replica of the Dehavillan dash 8 Q400 (402) I am antiscipating a prop length of between 8 and 10 inches. I plan to gear for a lower rpm and may use additional forces to add to the torque and thrust of the plane. I have to work out the weight issue as well as the wing loading as these planes(commercial turbo-props ) had a very narrow wing.
What compromises I will have to make along the way will determine the use of a scale prop (6 rather unique blades).
thanks again to all and please keep following this thread and add to it when you feel a need.
peterpont
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Old Dec 13, 2006, 12:37 AM
Dance the skies...
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United States, MA, Walpole
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Quote:
Originally Posted by cyclops2
<snip>

What plane used 6 bladed props ?
How about this one.
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Old Dec 13, 2006, 01:04 AM
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Christchurch, New Zealand
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Well, one possible advantage of the heli tail grips idea is that you could do variable pitch, which could save quite a bit of power getting enough thrust for takeoff.

So, I ran the numbers on a 5% Q400.

I assumed a 1.42m wingspan, 15.77dm^2 wing area, and 1950g all-up weight.

It seems if you use T-Rex 600 tail grips and blades to make 9.45x9 6-blade props, and you use something like a pair of Hyperion Z3025-12s direct drive on 3s2p 1800mAh lipo (or one 3s 1800 pack per motor, equivalently), you get a plausible model. It will probably need flaps, with a 13.1m/s (47kph, 29mph) stall speed clean, but it'll fly around for about half an hour at optimum cruise (4.5 minutes WOT), and top out at around 30m/s (108kph, or 67mph). Sounds nice to me.

However, variable pitch would be a big win; by going VP with a range from 6" to 13", you could probably ditch half the battery capacity, drop the stall speed to 12.5m/s, and at the same time increase the top speed by 20%... and still keep 22 minutes of duration. You'd also get the option of a bit of reverse pitch for braking, and even the ability to make the cool pitch-sweep sound big turboprops make as they do their taxi checks.
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